1. Field of the Invention
The present invention relates to a method for manufacturing a lignin for continuous carbon fiber spinning by a heat-fusion process, employing lignin as a starting material, which is contained in woody material in an amount of about 20 to 30%.
Nowadays comprehensive studies are being made on separation or modification of cellulose, hemicellulose and lignin from woody resources for the purpose of utilizing such materials as food, forage, and chemical industrial starting materials. In certain fields, development for industrialization is going on. In the field of pulping technology, new organic solvent digestion processes are extensively studied, where an alcohol, a phenol, acetic acid, or the like are used as the digesting agent. However, success of these new technologies depends upon the accomplishment of effective utilization of lignin.
2. Description of the Related Arts
One technology of converting lignin to industrial materials of high added value relates to manufacture of carbon fiber therefrom.
One prior art publication regarding lignin carbon fiber relates to lignin-poval type carbon fiber proposed by Professor Ohtani of Gumma University on 1963. See Japanese Patent Publications No. 15727/1966, and No. 26356/1967. This process is characterized by drawing out thread from a spinning solution prepared by heating and dissolving lignin (of industrial grade) and polyvinyl alcohol in a highly concentrated aqueous NaOH solution. This process was replaced by PAN type and pitch type carbon fiber because of the cost and the properties. After 20 years therefrom, the present inventors proposed a process for manufacturing lignin for continuous spinning by hydrogenolysis, and heating lignin obtained by digestion and explosion-disintegration of wood, as well as a process of producing carbon fiber therefrom. See Japanese Laid-Open Patent Application No. 110922/1987. The carbon fiber of the former process has disadvantages such that the manufacturing cost is high because of the wet spinning process and high temperature treatment at 1400.degree. C. or higher for vaporizing-off sodium, and the product is significantly low in strength characteristics. The latter of the above processes is now under study for industrialization. This process involves the problems of high capital cost resulting from high energy consumption and use of pressure vessels in hydrogenolysis in the spinning-lignin preparation process, and low yield of the carbon fiber.